1. Field of the Invention
The invention broadly relates to methods and compositions for controlling the flow of water in a subterranean formation. The invention more specifically relates to the use of a binding polysiloxane coating in a method of controlling the flow of water in a subterranean formation.
2. Description of the Related Art
Most hydrocarbon producing subterranean formations contain water, as well as hydrocarbons. This water becomes a problem when it is mobile. Unwanted water production is a continuing problem for the oil and gas industry as the presence of mobile water in the subterranean formations unfortunately leads to recovery of a fair amount of water along with the desired hydrocarbons. When water is recovered along with hydrocarbons, both have to be pumped from the formation to the surface, where the water has to be separated from the hydrocarbons and disposed of appropriately. If the water volumes are too high the cost of capturing and discarding the water can make continuation of hydrocarbon recovery cost prohibitive, likely resulting in production termination.
The influx of water into the hydrocarbon producing formation can be from, but not limited to, water flowing through fractures, thief zones and high permeability streaks or water coning. A relatively effective method of reducing the flow of unwanted water is by the mechanism of gellation and/or polymerization of a soluble silicate, such as sodium silicate. This type of process is referred to as chemical grouting, which is generally a process of injecting a chemically reactive solution that behaves as a liquid, but reacts within a pre-determined time frame to form a solid or gel in the subterranean formation.
Soluble silicate has found wide applications in water control. It is a permanent, nonselective product for sealing reservoir porosity and modifying permeability. It works by precipitating sodium silicate to create an amorphous, non-crystalline, ringing gel. The liquid sodium silicate can be made to gel and set in desired time frame (minutes to hours) by controlling the type and concentration of setting agent(s) or activator(s). The most common activators are acid, alkaline earth salts, glyoxal, and formamide. Soluble silicate is most effective when squeezed into perforations, whereas if it is left in the wellbore, the resultant gel plug is temporary and can be broken by tripping pipe through it. Experience shows that a very low break-through pressure can break the rigid gel in a core plug, which indicates a loose blocking mechanism of the silicates. In general, the rigid gel formed by the sodium silicate is somewhat prone to cracking and shattering when pressure is applied across a large cross sectional area.
While the use of sodium silicate in water control is somewhat effective, there is a need to further improve the chemistry of the gellation of sodium silicate to make soluble silicate a more effective water control system. It would be advantageous if the sodium silicate could withstand higher pressures than it is currently able yet still continue to reduce permeability.